Testing Queueable Apex

To test Queueable Apex, we follow the same pattern we have used for all our asynchronous code. We place the System.enqueueJob call between a Test.startTest method call and a Test.stopTest method call to run the asynchronous process synchronously:

@isTest
private class ExampleQueueable_Test {
    @isTest
    private static void testExecute() {
        Test.startTest();
        System.enqueueJob(new ExampleQueueable());
        Test.stopTest();
        //Assert on expected changes
    }
}

Note that if you were to run the following code:

@isTest
private class ExampleQueueable_Test {
    @isTest
    private static void testExecute() {
        Test.startTest()...